Like you I find playing around with SL pretty interesting for recreational coding. One of the experiences that made me think there was something to it was trying to code a working clock in a sandbox (a general building area in SL). Other avatars would walk past and make suggestions and as there's a fair few coders around it soon turned into an interesting collaborative effort. If only it was that simple in RL. Some things just work really neatly in SL - I once implemented a swarming algorithm using a flock of 'birds' as the objects (which gives a whole new take on oops).
As to resources - assuming you're beyond basic coding level then you should be able to figure most things out from the LSL Wiki - http://wiki.secondlife.com/wiki/LSL_Portal.
There's an ebook - "Scripting Recipes for Second Life" by Jeff Heaton which covers the basics in a reasonably well laid out way. It's only a few dollars but probably only worth it if you've not done a great deal of coding elsewhere. There's also regular classes held in-world, but I believe most of these are at a pretty basic level.
For groups I've always found the Scripters of Second Life group very helpful with a lot of people generally on it. There's one called simply Scripts which is quite active too.
A couple of words of warning, LSL, whilst Turing-complete is pretty broken in several areas, lacks modern program constructs (and some older ones - like arrays!) and much of the 'black-art' of LSL is knowing how to work around the limitations, With the advent of Mono though this is likely to be a decreasing issue.
Also there does seem to be an assumption by the Lindens that if you want to do any 'heavy-lifting' code you'll do it on a server off-world and call and return results to/from SL. This isn't helped by the XMP-RPC implementation being very broken, although HTTP works fine (and generally better than might be expected).
